Spark plug for receiving a pressure sensor and corresponding spark plug connector

ABSTRACT

A spark plug for accommodating a pressure sensor. A connecting channel for extending a connecting line of the sensor extends in a housing and in a central section of the insulating core of the spark plug. As a result of this setup, the connecting line is extended in a protected manner in the region of the spark plug.

FIELD OF THE INVENTION

[0001] The present invention relates to a spark plug including aninsulator core that extends along the longitudinal axis of the sparkplug. The insulator core becomes narrower on one side from a centralsection to an insulator nose. The central section and the insulator noseare enclosed by a spark plug housing which, in the region of theinsulator nose is configured as an axially extending threaded sleeveincluding an outer thread. In the threaded sleeve a sensor accommodatingchamber is left open for accommodating a sensor element. A connectingchannel formed in the threaded sleeve extends from the sensoraccommodating chamber, approximately parallel to the longitudinal axisof the threaded sleeve and on to an outer side of the housing.

BACKGROUND INFORMATION

[0002] A spark plug including a pressure sensor built into the sensoraccommodation chamber is referred to in Japanese Patent Application No.092 600 24. In this spark plug, the other end of the connecting channellies in the edge region of a middle housing part. A connecting electrodeis fastened laterally on a nut configured on the housing, for screwingin the spark plug. In this spark plug, the connecting channel runs orextends to the outside at an angle from the transition between thehousing sleeve and the middle portion of the housing.

[0003] Other spark plugs including pressure sensors in the housingsleeve are referred to in U.S. Pat. No. 4,969,353 and PCT ApplicationNo. 9731251. In the case of the spark plugs discussed there, theconnecting channel also extends to the outside at an angle in the middleportion of the housing.

SUMMARY OF THE INVENTION

[0004] The present invention involves the problem of improving sparkplugs including sensors built into housing sleeves. In addition, thepresent invention describes a spark plug connector which is suitable,particularly, for connecting an ignition cable and a supply line for thesensor to the improved spark plug.

[0005] The present invention uses the following considerations as abaseline. If the end of the connecting channel lies at a lateral surfaceof the spark plug housing, additional space is required for extendingthrough the connecting cable which connects the sensor element to asensor circuit. If the connecting cable, which is relatively thincompared to the ignition cable, is extended laterally toward the outsidein a section of the connecting channel, a large gap is created betweenignition cable and connecting cable. This gap has the result that theconnecting cable has to be extended separately from the ignition cableover a longer section. The result of this is that, when the spark plugis installed into the engine block, it is easy for the connecting cableto become jammed between the wrench and the screw formed on the sparkplug. Even if the ignition cable is connected to a connecting electrodeonly after the spark plug is screwed into the engine block, damage tothe connecting electrode may occur during the installation. The sectionin which the connecting cable of the sensor is extended separately fromthe ignition cable lies exposed in the engine block even after theinstallation of the spark plug and the connection of the connectingcable.

[0006] Therefore, the spark plug according to the present invention isconfigured, in addition to the features described at the beginning, insuch a manner that a section of the connecting channel extends in thecentral section of the insulating core.

[0007] The connecting channel exits on the side of the housing lyingclosest to the terminal for the ignition cable and/or from the insulatorcore. By this measure, the connecting channel, and thereby also theconnecting cable accommodated in the connecting channel may be extendedin the entire region of the housing near the ignition cable or at thelongitudinal axis of the spark plug. The outlet of the connectingchannel lies very close to the longitudinal axis of the spark plug, e.g.at a distance of less than 10 mm, preferably less than 5 mm. It isachieved by these measures that the exposed section of the connectingcable is further shortened in comparison to other spark plugs. As aresult of this centrally lying exit, the exit may be positioned directlybelow the spark plug connector, or even within the spark plug connector.In either case, there is no longer an exposed section of the connectingcable. Therefore the spark plug according to the present invention mayallow for a protected extension of the connecting cable along its entirelength, or at least in regions which are exposed to mechanical effectswhen the spark plug is installed.

[0008] In one exemplary embodiment of the present invention, theconnecting cable extends in the central section of the insulating core,approximately parallel to the longitudinal axis of the spark plug. Ifthe connecting channel is also extended in the central section of theinsulating core, parallel to the longitudinal axis or at aninsignificant inclination of 1 or 2°, for example, kinks may be avoidedover the length of the connecting channel. The connecting channelextends exactly so that a connecting cable in the connecting channeldoes not kink, and is easy to install.

[0009] In an alternative configuration, the connecting channel extendsin the central section of the insulating core at an angle to thelongitudinal axis of the spark plug, at an angle between 10° and 5°. Theangle may allow for the connecting channel to be placed in the region ofthe insulating core without costly special tools, e.g. with the aid of a(grinding) broach. On the other hand, the angle should not exceed 10°,since otherwise a connecting channel extends outwards at an angle endstoo far removed from the ignition cable. On the other hand, a connectingchannel extending inwards at an angle is no longer completely insulatedby the insulator core.

[0010] The positioning of the connecting channel at an angle has theresult that, in the longitudinal direction, at the transitions betweenthe housing and the central section, the connecting channel is easilybent. The bend is less than 10° or less than 5°. When the bendingamounts to so little, a protective sleeve and/or the connecting cablemay still be easily installed in the connecting channel.

[0011] In a next configuration, the end of the connecting channel liesbetween the insulating core and the housing. Particularly in the case ofspark plugs which also become narrower in the direction of theconnection for the ignition cable, it is achieved by this measure thatthe connecting channel has to be extended only in a comparatively shortsection of the insulating core. Thus, the connecting channel may beextended through the same opening in the housing through which theinsulating core is also extended. If necessary, a small notch is formedat the opening in the housing which surrounds the insulating core.

[0012] If the other end of the connecting channel lies close to theinsulator core, at a distance of less than 5 mm, a connecting cable maybe extended directly from the end of the connecting channel into a sparkplug connector, and is thus protected over its entire extension.

[0013] In one exemplary embodiment, the sensor element ispressure-sensitive, so that the sensor signal is a function of thepressure acting upon the sensor element. A piezoelectrically, apiezoresistively or an electrodynamically functioning sensor element isused. Optical sensors are also available. At the present time, sensorelements are on the market which may be installed in the threaded sleeveof the spark plug even if the threaded sleeve has the usual dimensionsused for spark plugs up to the present. The positioning of the centerelectrode and the ground electrode, as well as the coefficient of heattransfer agree with the positioning and the coefficient of heat transferof the original spark plug. The combustion properties and the pressurecharacteristic in the combustion chamber agree among the productionspark plugs used up to now and the spark plug including a pressuresensor. In particular, the “breathing” properties of the spark plugremain unchanged.

[0014] In a next further development, the insulating core becomesnarrower from the central section towards a terminal for an ignitioncable. Thus, the central section has the largest diameter and is usedfor fixing the housing.

[0015] The present invention also describes a spark plug connector whichis suitable especially for the spark plug according to the presentinvention or its further exemplary embodiment. The spark plug connectorincludes a housing configured mostly in one piece, in which is locatedlead-through for an ignition cable. In the spark plug connectoraccording to the present invention, besides the lead-through for theignition cable, there is an additional lead-through for accommodating aconnecting line for a sensor element arranged in the spark plug. If theoutlet port of the connecting channel is at a distance from thelongitudinal axis of the spark plug which is less than the radius of thespark plug connector, the connecting line may be extension protectedover its entire extension to the sensor element. Inside the spark plug,the connecting line is extended in the housing and in the insulatingcore. Outside the spark plug, the connecting line is extended betweenthe insulating core and the spark plug connector. In the area of thespark plug core, the relatively thin connecting cable may then beconnected, for example, to a thicker cable via a plug connection whichmay include, for instance, a non-removable sheathing and a protectivescreen.

[0016] In another exemplary embodiment of the spark plug connector, thelead-throughs are arranged eccentrically with respect to thelongitudinal axis of the spark plug connector. Due to this measure, thespark plug connector may be manufactured having a small diameter, asufficient distance between the ignition cable and the connecting lineof the sensor element being nevertheless ensured.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 shows a spark plug in a side view and a partial sectionalview.

[0018]FIG. 2 is an enlarged illustration of a connecting channel in theregion of a threaded sleeve of the spark plug.

[0019]FIG. 3 is an enlarged illustration of the connecting channel inthe region of the insulating core of the spark plug.

DETAILED DESCRIPTION

[0020]FIG. 1 shows a spark plug 10, which has the usual dimensionsexisting to date. A spark plug connector 12, which is used forconnecting an ignition cable 14 and a connecting line 16, is pluggedonto spark plug 10. Ignition cable 14 carries an ignition voltage of upto 40 kV and is screwed onto connecting stud 18. Connecting line 16 isused for carrying the signal coming from a pressure sensor 20. Thevalues of this signal are at the most 12 V, for example. In the regionof spark plug connector 12 there is arranged a connecting element 24,e.g. a plug connecting element, with the aid of which a connecting wire26 and connecting line 16 are electrically connected to each other.

[0021] A metallic spark plug housing 28 encloses the lower part of aninsulator core 30, which is made of a ceramic material. Insulating core30 becomes narrower from a central section 32 to its end. At the upperend of insulating core 30 connecting stud 18 is positioned. Betweenconnecting stud 18 and central section 32, creeping current barriers 34are expediently formed on the surface of insulating core 30.

[0022] In a downward direction, insulating core 30 becomes narrower downto an insulator nose 36 which insulates a center electrode 38. Centerelectrode 38 is connected to connecting stud 18 in an electricallyconducting manner.

[0023] At housing 28 there are formed in this sequence a screw-in nut40, a central housing part 42 and a housing sleeve 44, which eachenclose insulating core 30. Above threaded nut 40, an edge 46 bentinwards encloses central section 32 of insulating core 30. Threaded nut40 is hexagonal, for instance, and may be screwed using a usual plugwrench. Between threaded nut 40 and central housing part 42 there is acircumferential groove 48. Below central housing part 42 there is asealing ring 50 which is used for sealing one combustion chamber in theengine block. Housing sleeve 44 bears an outer thread 52 which matchesan inner thread (not shown) in the engine block Connecting thread 52 isan outer thread, for example. At its end, housing sleeve 44 carries atop electrode 54 which is bent inwards, and thus forms a spark gap ofpredefined width between center electrode 38 and top electrode 54. Atthe free end of housing sleeve 44 there is an accommodation chamber 56for accommodating pressure sensor 20. Accommodation chamber 56 iscylindrical. The longitudinal axis 58 of this cylinder is parallel tolongitudinal axis 60 of the spark plug. In principle, longitudinal axis58 of this cylinder could also lie at an angle to longitudinal axis 60of the spark plug.

[0024] From accommodation chamber 56 a connecting channel 62 extendsparallel to longitudinal axis 60, in the direction of connecting stud18. In central section 32 of insulating core 30, the connecting channelextends approximately parallel to longitudinal axis 60. Connectingchannel 62 is coated using an inserted protective casing 64. Protectivecasing 64 sheathes connecting wire 26 in the region of spark plughousing 28.

[0025] The course of connecting channel 62 in the region of the sparkplug housing and in central section 32 of insulating core 30 isdescribed with reference to FIGS. 2 and 3.

[0026] During the production of spark plug 10, the lead-through forconnecting channel 62 in central section 32 is first put into insulatingcore 30, for example, by grinding using a (grinding) broach. Only thenis insulating core 30 connected to housing 28. The lead-through forconnecting channel 68 in housing 28 is inserted before or afterconnecting housing 28 to insulating core 30, for instance by drilling.Protective sheathing 64 is inserted before connecting housing 28 andinsulating core 30. Subsequently, sensor element 20 and connecting wire26 are applied and cemented in, in a gas-tight manner.

[0027]FIG. 2 is an enlarged illustration of connecting channel 62 in theregion of threaded sleeve 44. The reference numerals shown in FIG. 2corresponds to the reference numerals already described in reference toFIG. 1.

[0028] Accommodation chamber 56, connecting channel 62 and protectivesheathing 64 in the illustrated region are aligned with respect tolongitudinal axis 58 of connecting channel 62. The diameter ofconnecting channel 62, in this example, is less than the diameter ofaccommodation chamber 56. In the region of protective sheathing 64, thediameter of connecting channel 62 is somewhat greater than in region 80which lies directly at accommodation chamber 56 and is not surrounded byprotective sheathing 64. An offset 82 is used as a stop when protectivesheathing 64 is plugged into connecting channel 62.

[0029] Accommodation chamber 56 is closed off by a closure diaphragm 84.In addition, FIG. 2 shows a sealing element 86 extending aroundlongitudinal axis 60, which lies between insulating nose 36 and housingsleeve 44. Center electrode 38 ends in a region filled with a glassmelt.88. Glass melt 88 forms an electrical resistor in the milliohmrange (kiloohm range is also allowed) between center electrode 38 and anelectrode 90 that leads to connecting stud 18.

[0030]FIG. 3 is an enlarged illustration of connecting channel 62 in theregion of central section 32 of insulating core 30. The referencenumerals shown in FIG. 3 corresponds to the reference numerals describedin reference to FIG. 1.

[0031] Connecting channel 62 first of all enters from central housingpart 42 into an inner chamber 90 enclosed by spark plug housing 28. Atthe entry point into or the exit point from center part 42, the courseof connecting channel 62 is buckled by an angle W1, which amounts toabout 5°. Between central housing part 42 and insulating core 30,connecting channel 62 is formed by protective sheathing 64. Due to theextending of connecting channel 62 in insulating core 30, a region 92 ofinsulating core 30 is created which lies between connecting channel 62and housing 28. Connecting channel 62, in the region of edge 46, isbuckled by an angle W2, for instance by an angle of about 9°.

What is claimed is:
 1. A spark plug for accommodating a pressure sensor,having: an insulating core (30), extending along the longitudinal axis(60) of the spark plug (10), which narrows down on the one hand from acentral section (32) to an insulating nose (36), a housing (28)enclosing the central section (32) and the insulating nose (36), whichis designed, in the region of the insulating nose (36), as an axiallyrunning housing sleeve (44), a sensor accommodation chamber (56) in thehousing sleeve (44) for accommodating a sensor element (20), and aconnecting channel (62) formed in the housing sleeve (44), which extendsfrom the sensor accommodation chamber (56) approximately in parallel tothe longitudinal axis (60) in the housing sleeve (44), and beyond thatto the outside of the spark plug (10), wherein a section of theconnecting channel (62) runs in the central section (32) of theinsulating core (30), and the connecting channel (62) exits on the sideof the housing lying closest to a connecting stud (18) for an ignitioncable (14) and/or exits from the insulating core (30).
 2. The spark plug(10) as recited in claim 1, wherein the connecting channel (62) in thecentral section (32) of the insulating core (30) runs approximatelyparallel to the longitudinal axis (60).
 3. The spark plug (10) asrecited in claim 1, wherein the connecting channel (62) in the centralsection (32) of the insulating core (30) runs at an angle to thelongitudinal axis (60), preferably at an angle between 3° and 10°. 4.The spark plug (10) as recited in claim 3, wherein the connectingchannel (62) is bent slightly in the longitudinal direction at thetransitions between the housing (28) and the central section (32),preferably by less than 10°, or less than 5°.
 5. The spark plug (10) asrecited in one of the preceding claims, wherein the other end of theconnecting channel (62) lies between the insulating core (30) and thehousing (28).
 6. The spark plug (10) as recited in one of claims 1through 5, wherein the other end of the connecting channel (62) liesnear the longitudinal axis (60), preferably at a distance of less than 5mm.
 7. The spark plug (10) as recited in one of the preceding claims,wherein the sensor element (20) is pressure-sensitive and preferablyincludes an optically, a piezoelectrically, a piezoresistively or anelectrodynamically functioning element.
 8. The spark plug (10) asrecited in one of the preceding claims, wherein the insulating core (30)becomes narrower from the central section (32) to a connection for anignition cable.
 9. The spark plug (10) as recited in claim 8, whereinthe connecting channel exits at an edge (46), bent inwards, of thehousing (28), which encircles the central section (32).
 10. A spark plugconnector (12), especially for a spark plug (10) according to one of thepreceding claims, having a housing and having a lead-through for anignition cable (14) in the housing, characterized by a lead-through foraccommodating a connecting lead (16) for a sensor element (20) situatedin the spark plug (10).
 11. The spark plug connector (12) as recited inclaim 10, wherein separate lead-throughs for the ignition cable (14) andthe connecting line (16) are provided; or a common lead-through isprovided for the ignition cable (14) and the connecting line (16). 12.The spark plug connector (12) as recited in claim 10 or 11, wherein thelead-throughs are positioned eccentrically with respect to thelongitudinal axis (60) of the spark plug connector (12).